Furnace and method of operating the same



April'8, 1930. 1. a. COG' L' N n m. 1,153,363

FURNACE AND METHOD .OF OPER ATING THE SAIE Original Filed July 21, 1 923 INVENTORs Afl'ORNEU the usual manner.

' wardly Patented Apr. 8, 1930 UNITED STATES PATENT OFFICE THOMAS G. COGHLAN, OF ELI EZABETH, AND EINAR A. JOHNSEN', 0F MOUNTAIQN" LAKES,

JERSEY FURNACE AND METHOD OF OPERATING THE SAME Original application filed July 21, 1925, Serial No. 44,957. Divided and this application filed June 5, 1926.

Serial No. 113,856.

Our present invention relatesto furnaces, particularly furnaces for use with solid fuel and in connection with steam boiler, and methods for operating such furnaces, and

will be best understood from the following. description, and the annexed drawings of an diagrammatic, of the boiler and furnace,

showing the exterior combustion air supply system.

Like reference characters indicate like parts throughout the drawings.

In the illustrative embodiment, the steam boiler which we have chosen for purposes 0 illustration, is-provi ded with water: tubes 10, uptake headers 11, downtake headers 12 and a steam and water drum 13, all connected in Baflies 14 and 15 direct the gases entering at the bottom of the first pass adjacent the uptake headers, back and forth across the water tubes to the gas exit 16. The combustion chamber is formed so as to have a narrow mid-section. In the lower part of the combustion chamber is a chain grate stoker 17 which receives its fuel from a hopper in the usual manner, and carries it to the right, the ashes being deposited in the usual ash hopper through the opening 19.

' At the front of the stoker 17 are a pair of- .curved arches 20 and 21, the latter projecting over the forward part of the rate to form a combustion arch therefor. S1milarly, at the rear of the chain grate stoker'l'i' is an arch 22 and an arch 23, the latter also forminga combustion arch or roof extending well forover the rear end of the stoker. The inner ends of the arches 21 and 23 are curved so as to provide a narrow assa'ge 24 into which the gases from the sto or are directed by the arches 21 and 23.

The-passageway 24 merges into a combustion chamber 25 which pre erably is provided with upwardly and outwardly diverging walls, the chamber 25 preferably having a fiat roof 26 suspended over it with a gas outlet 27 at one side of the first pass of the boiler.

roof 26 leading into the At each side ofthe widened part of the I I narrow passage 24 are auxiliary combustion air inlets arranged to direct the air crosswise of the passage. 'Aseries-of nozzles 28 extend across the'furnace side by side, the rear end of each of the nozzles communicating with an airduct 29 on each side of the passageway 24. I

The combustion air supply for the furnace is shown, in which an air heater 34 of any of the well-known types heats the combustion air entering the air heater through the duct 35. The heated air then flows through the duct 36 to and through the fan 37 and a feed water heater or economizer 45 into a duct 38 which communicates with spaces along the f stoker 17 and between the runs thereof to supply the usual combustion air flowing through the fuel also a duct 39 which communicates with the ends of each of the ducts 29 from which the air flows through the nozzles 28 into the narrow passage 24:. Dampers in the several ducts are provided so that the amount of air delivered to any part of the furnace can be controlled. o

With the arrangement described, the fur nace is preferably operated as follows Air is supplied th ough the duct'38 at pressures insufiicient to lift the heavier particles of the fuel from the bed, but insufficient quan tities to burn the solid fuel on the grate. The amount supplied, however, is insufiicient to complete the'combustion of the gases rising, Such incompletely burned gases, together with the finer particles of fuel,

from the grate.

are directed by the arches'21 and '23 to the narrow'passage 24:, from which they expand through thenarrow passage 24 combustion chamber 21$,minglingl ditional combustion air" from e nozzles 28,; this auxiliary or additional combustion air being supplied in sufficient quantity to, complete the combustion of the gases and fine particles of fuel. By bringing all of these gases and fine-particles into a comparatively narrow space, the additional airis thoroughly mixed therewith so that as these into the with adon the grate. From the fan37 leads 40 brought together in a small space and the.

rangement, any possible Stratification of the gases and air rising from the grate, which Stratification occurs in furnaces as heretofore made, is entirely avoided by dlrectmg all of the gases and air passing through the grate into the narrow throat. By forming the combustion chamber 25 as shown, the gases therein are given a turbulence which com letes the mixing of the air and gases, whic mixing is aided by the provision of the gas outlet at one side of the combustion chamber.

We have found from experience with this type of furnace and with the method of operation as described above, that the amount of air supplied can be regulated close to the theoretical amount of air required for the complete combustion of the fuel, without any appreciable amount of excess air. In practically all cases, the quantity of air supplied through the grate is larger than that supplied through the nozzles 28. Preferabl we arrange the dampers in the ducts 38 lea ing to the spaces beneath the fuel bed so that little or no air passes through the fuel at the front and middle portions of the grate and so that a somewhat larger quantity of air flows through the rear end of the grate, the

quantities of air that do pass through the grate being such a to' be used up largely in the burning of the solid fuel on the grate. Consequently, the gases which enter the narrow throat. 24 are partly unburned combustible gases.

In the narrow throat 24, the unburned gases and the auxiliary combustion air are subse uent expansion into the upper combustion to amber intimatel the combustion isthere pleted. Thepassin narrow passage 24 between the larger spaces below and above the passage acts like a Venturi tube, so that there is substantially no substantially comincrease of draft resistance, the pressure, at

least under some conditions, being lowerin the passage 24 than it is in the upper and the lower parts of the combustion chamber.

By arranging the roof arch 23 in the manner shown, we have found that a large part of the relatively fine particles of burning fuel that may be carried up from the rear end of a the fuel bed b the' combustion air supplied beneath it, is t rown forwardl and down on the incoming fuel and there y aidin the igniting of the fresh fuel, instead of eing carried u into the upper combustion chamber, the s ope of this arch being arranged to produce this effect. 7 v

We preferably operate the fiirnace so that the pressure at the narrow passage 24 is'n'egmixes the two and of the gases through the- I pipe 46.

of .the abstraction of some of its heat b arches 21 and 23. These arches preferably are suspended in a Well-known manner on metallic members on which the tile are suspended, these metallic members, in turn, being supported on hangers connected to the ironwork of the ducts. We have found that the cooling effect of the ducts 29 is such that arche can be maintained over the fuel bed which would otherwise be impossible, and the heat carried away from the walls of the air ducts 29 by the air is recovered and returned to the furnace.

As is well known, it is advantageous to supply the combustion air in a heated condition, ut particularly where this heated air is supplied through a grate, it is necessary, in order not to destroy the grate, to keep the temperature of the heated combustion air below certain limits. On the other hand, in order to complete the combustion of gases, as, for instance, in the upper part of the furnace 25, it is desirable to have the combustion'air heated to as high a degree as possible. In

the arrangement which we have illustrated, 9

the temperature ofthe air supplied beneath the grate 17 is lower than the temperature of the air supplied through the nozzles 28, because this additional air supplied through the nozzles '28 receives additional heat as it flows through the ducts 29.

Preferably, we heat the air directly from the flue gases as they emerge from the boiler and this produces a temperature too high to be used directly under the grate. In such cases, the temperature of this part of the air may bereduced by abstracting some of the heat from this portion of the combustion air by passing this heated air over the feed water heater or an economizer 45, the feed water being delivered to the drum l3 through the With this arrangement, the air from the heater 34 may be heated to any desired degree, and it will be delivered at substantially this high temperature to the nozzles 28. But the portion of this heated air which is delivered beneath the grate will be at a considerably lower temperature by reason the economizer or feed water heater. It will be understood that the temperature of the air supplied beneath the grate may be reduced to any desired extent by regulating the flow of the water past the heating surface of the water heater or economizer and thereby varying the amount of heat abstracted from the air, such re llation being effected, in the form illustratec by by-passing more or less of the feed water through the pipe 47.

The arrangement illustrated by which the combustion air is heated directly by the boiler waste gases without reducing the temperature of the gases by an economizer or the like, and

then transferring some of the heat'to the boiler feed water before supplying the air to the fuel is advantageous irrespective of the particular way in which. the air is used. In such an arrangement, the heating surfaces of the economizers are contacted only with clean and relatively dry air instead of with the (lust-laden products of combustion, so that may be used-with or without other features,

' therein, ducts to lead the remainder of the as desired.

We claim: 1. The method of operating a boiler furnace having a fuel grate in its lower part,

which comprises heating all of the combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream by transferring some of its heat to the boiler feed water, supplying the air of reduced temperature beneath the grate and supplying the heated air from the other stream to the gases rising from the fuel on the grate at a point above the grate.

2. The method of operating a boiler furnace having a fuel. grate in its lower part, which comprises heating all of the combustion air to a high "temperature, dividing the 40 heated air into two streams, reducing the temperture of one stream by transferring some of its heat to the boiler feed water, supplying the air of reduced temperature'beneath the grate, causing the gases rising from the grate to flow together into a restricted space above the grate, supplying the heated air from the other stream tothe gases as they pass through the restricted space and then permitting the mingled air and gases to expand into a larger combustion chamber to complete the combustion of the gases.

3 A steam boiler, a furnace to supply heated gases to the boiler, an air heater heated by. the waste gases from the boiler, an economizer connected to the boiler, a duct to lead some of the heated air from the air heater to one.

part of the'furnace, and ducts to lead the remainder of the air to the economizer and from the economizer to another part of the furnace.

4. A steam boiler, a furnace therefor having a fuel grate therein, an air heater heated by thewaste gases from the boiler, an economizer connected to the boiler, a duct to lead some of the heated air from the air heater to the furnace at a point above thegrate therein, aird ducts to lead the remainder of the air from the air heater over the economizer to the furnace at a point beneath the grate therein. a

5. A steam boiler, a furnace to supply heated gases to the boiler, an air heater heated by the waste gases from the boiler, an'economizer connected to the boiler, a duct to lead some of the heated air from the air heater to one part of the furnace, ducts to lead the remainder of the air to the economizer and from the economizer to another part of the furnace, and means whereby the cooling effect of the economizer on the airpassing therethrough may be varied.

6. A steamboiler, a furnace therefor having a fuel grate therein, an air heater heated by the Waste gases from the boiler, an economizer connected to the boiler, a duct to lead some-of the heated air from the air'heater to the furnace at a point above the grate air from the air heater over the economizer to the furnace at a point beneath the grate therein, and means whereby the cooling eftherethrough may be varied.

7. In combination, a steam boiler, a furnace therefor having a fuel grate therein, an air heater heated by the waste gases from the boiler, an economizer connected to the boiler, a duct to lead some of-the heated air from the air heater to the furnace at a point above the-grate therein, ducts to lead the remainder of the air from the air heater over the economizer and todischarge it at a plurality of points beneath the grate, and means to regulate the discharge of the air at said points.

fect of the economizer on the air passing 7 8. The method of operating a furnace which comprises-supplying a fuel to a combustion chamber, heating air, directing part of said air into said chamber, extracting some of the heat from the remainder of sa1d air, anddirecting said remainder to the place at which said fuel is supplied to the chamber.

9. The method of operating a furnace which comprises supplying a fuel to a combustion chamber, heating air by the gases from said chamber, directing part of said air into said chamber, extracting some'of theheat from the remainder of said air, and directing said remainder to the place at which I said fuel is supplied to the chamber.

i 10. The method of operating a furnace which comprises supplying fuel to a grate in a combustion chamber, heating air, directln part of said air into saidchamber above sa1 grate, extracting some of the heat from the remainder of sald' air, and directing sald remainder beneath said grate.

11. The method of operating a boiler furnace having fuel burning mechanism therein which comprises heating all of the combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream by transferring some of its heat to the boiler feed water, supplying the air of reduced temperature to said mechanism, and supplying ;the heated air a 5 from the other stream to the gases coming from said mechanism. I 12. The method of operating a boiler furnace. having fuel burning mechanism which comprises heating allofthe combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream by transferring some of its heat to the boiler feed water, supplying the air of reduced temperature to said mechani'sm, causing the gases coming from said mechanism to flow together into a restricted space, supplying the heated air from the other stream to the gases as they pass through the restricted space, arid then permitting the g mingled air and gases to expand into a larger combustion chamber'to complete combustion of the ases.

13. T e method of operating aboiler furnace having fuel burning mechanism which comprises heating all of the combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream by transferring some of its heat to the boiler feed water, supplying the air of reduced temperature to said mechanism, causing the gases coming from said mechanismto flow together into a restricted space, and supplying the heated air from the other stream to the gases as they pass through the restricted space.

. 14. The method of operating a boiler ,furnace having fuel burning mechanism therein which comprises heating all-of the combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream, supplying the air of reduced temperature to said mechanism, and supplying the heated air from the other, stream to the gases coming from said mechamsm.

15. The method of operating a boiler furnace having fuel burning mechanism which comprises heating all of the combustion air to a high temperature, dividing the heated air into two streams, reducing the temperature of one stream, supplying air of reduced temperature to said mechanism, causing the gases coming from said mechanism to flow together into a restricted space, supplyingthe heated air from the other stream to the gases as they pass through the restricted space, and then permitting-the mingled air and gases to expand into a larger combustion chamber to complete combustion of the gases.

THOMAS G. COGHLAN. EINAR A. JOHNSEYN. 

